Paper stickers to monitor pathogens are more effective than swabs

"The
porous structure of paper seems able to collect and accumulate [bacterial]
contamination," said first author Martin Bobal, technical assistant,
Christian Doppler Laboratory for Monitoring of Microbial Contaminants,
Department for Farm Animal and Public Health in Veterinary Medicine, The
University of Veterinary Medicine, Vienna, Austria. "This requires
mechanical contact, for example by hand, or by splashed liquids."

In the study, the
investigators, who specialize in monitoring cheese production, chose to target
the organism Listeria monocytogenes, a pathogen that commonly contaminates raw
milk and other raw dairy products, including soft cheeses such as Brie, Camembert,
and Feta. They used qPCR, a method of quantifying DNA samples to determine the
numbers of these bacteria, as well as of Escherichia
coli.

Surfaces
in food processing plants must be cleaned regularly. Unlike swabs, artificially
contaminated stickers provided a record of contamination that took place over
at least two weeks, despite washing, flushing with water, or wiping with
Mikrozid, an alcohol-based disinfectant, to simulate cleansing practices.
"Recovery [of DNA] from the stickers was rather variable, at around 30%,
but did not distinctly decrease after 14 days of storage," the report
stated. "This suggests the possibility of sampling over two weeks as
well."

In a
proof of concept experiment, the researchers placed stickers at multiple locations
that frequently undergo hand contact -- such as on light switches and door
handles -- for one to seven days. Both bacterial species were detected
repeatedly from these stickers.

Unlike
stickers, swabbing is impractical on complex surfaces, such as door handles,
light switches, and other fomites (objects likely to be contaminated with, and
spread infectious organisms) and does a poor job of taking up bacteria from dry
surfaces, according to the report.

"In
the food production facility, conventional swabbing as a standard method can
only expose a momentary snapshot," the investigators wrote. "For
example, it is not possible to reconstruct information about yesterday's status
after cleansing has been performed. In addition, when moistened swabs or contact-plate
sampling methods are used, they bring with them growth medium into a supposedly
clean environment, making subsequent disinfection necessary."

The
investigators showed that plain paper stickers could trap not only bacterial
pathogens and related DNA, but dead, and viable but non-culturable pathogens,
which also can pose a threat to public health.

"A
major advantage of stickers is in handling: they are easy to distribute and to
collect," the authors concluded. "We put the stickers directly into the
DNA-extraction kit's first protocol step. We did not encounter any inhibition
or loss of information during DNA-extraction, nor during qPCR," said Mr.
Bobal.